The present invention relates to a method of mounting a deflection unit on a cathode ray tube envelope.
The invention also relates to a combination of a cathode ray tube and a deflection unit made by said method.
Proposals for mounting deflection units are disclosed in U.S. Pat. Nos. 3,986,156 and 3,939,447. In the case of U.S. Pat. No. 3,986,156 an annular platform is bonded onto the external surface of the tube cone. A housing is mounted on the deflection unit. At positions disposed at 90.degree. of rotation about the Z-axis of the display tube, rigid members are disposed between and connect the deflection yoke to the platform. A test-pattern is displayed on the display tube and the position of the deflection unit is adjusted so that a correct test pattern is displayed and subsequently the rigid members are either bonded or ultrasonically welded in position. Such a mounting arrangement has three strong degrees of freedom and three weak degrees of freedom.
U.S. Pat. No. 3,939,447 discloses three embodiments of a yoke mounting means. In the simplest of these three embodiments the deflection unit is mounted in an annular housing with four cantilever springs extending therefrom. This assembly is placed on the neck of the display tube so that the free ends of the springs are in direct contact with the conical portion of the tube envelope. Each spring has a hollow post thereon which serves as a conduit for adhesive. After the deflection unit has been adjusted then the springs are bonded to the conical portion by adhesive introduced through the hollow posts. Optionally auxiliary coil springs may be attached between the posts and the display tube mounting means to minimize any shearing force between the cantilevered springs and the conical portion of the envelope caused by the pressure of the cantilevered springs which, due to the adjustment of the deflection unit, are under varying degrees of distortion. The use of adhesives to secure the springs to the envelope has a number of disadvantages with respect to the speed of fixing and the reliability of the respective joints.
These methods of deflection unit mounting do not lend themselves to being easily mechanized. For mechanisation of the deflection unit mounting it is necessary to be able to mount the deflection unit on the tube neck, adjust the unit to its optimum position to give a proper image and to fix the unit in this optimum position very rapidly. The mounting arrangement should be such as to provide shock resistance, thermal stability over the expected working life of the tube and only 6 degrees of freedom.